Note that this is an experimental feature in Hibernate 3.0 and is under extremely active development.
Hibernate lets you work with persistent XML data in much the same way you work with persistent POJOs. A parsed XML tree can be thought of as just another way to represent the relational data at the object level, instead of POJOs.
Hibernate supports dom4j as API for manipulating XML trees. You can write
queries that retrieve dom4j trees from the database and have any
modification you make to the tree automatically synchronized to the
database. You can even take an XML document, parse it using dom4j, and
write it to the database with any of Hibernate's basic operations:
persist(), saveOrUpdate(), merge(), delete(), replicate()
(merging is not yet supported).
This feature has many applications including data import/export, externalization of entity data via JMS or SOAP and XSLT-based reporting.
A single mapping may be used to simultaneously map properties of a class and nodes of an XML document to the database, or, if there is no class to map, it may be used to map just the XML.
Here is an example of mapping a POJO and XML simultaneously:
<class name="Account"
table="ACCOUNTS"
node="account">
<id name="accountId"
column="ACCOUNT_ID"
node="@id"/>
<many-to-one name="customer"
column="CUSTOMER_ID"
node="customer/@id"
embed-xml="false"/>
<property name="balance"
column="BALANCE"
node="balance"/>
...
</class>Here is an example where there is no POJO class:
<class entity-name="Account"
table="ACCOUNTS"
node="account">
<id name="id"
column="ACCOUNT_ID"
node="@id"
type="string"/>
<many-to-one name="customerId"
column="CUSTOMER_ID"
node="customer/@id"
embed-xml="false"
entity-name="Customer"/>
<property name="balance"
column="BALANCE"
node="balance"
type="big_decimal"/>
...
</class>
This mapping allows you to access the data as a dom4j tree, or as a graph of
property name/value pairs (java Maps). The property names
are purely logical constructs that may be referred to in HQL queries.